I have a new battery assembled and online for the last day or so. It has not drained down past 95%. I have one cell that drops to a delta of .37v compared to the others cells while under load. When the load is removed the cell bounces back. The rebound could be my Heltec managing the issue. Should I just run it down and recharge a few times and see what happens? Could the cell be bad or damaged? I did top balance as well as my current skill level would allow.
1 cell acting different in my 16s battery.
- Thread starter Darce
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I did top balance before I assembled the pack. Is there a way I can test the cell or do I just monitor it’s behavior through a few cycles?
ScoTTyBEEE
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Make sure the bus bar is tight and has good contact. Maybe take it off and clean everything.
MisterSandals
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And if not too difficult, swap cell 9 with cell 8 or 10 just for grins. It could help identify a balance wire crimp problem or connection problem. Unlikely but possible and maybe easy to do this test.
Shale MacGregor
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My experience is a bad contact. Check torque on every nut.
Ok I will check the bus bars, crimps and tighten everything back up. Hopefully one of those is the culprit.
I did not have time to swap the cells position but I did see that a couple ring terminals did budge a bit when I tried moving them. I re-torqued everything back down and it seemed better at first. Then on charge with full sun at 40 amps that same cell raced up to 3.65 and triggered the disconnect. All the other cells at 3.39 or so. The battery was mostly charged so I left it to see what happens with load on it overnight.
MisterSandals
Participation Medalist
You may have to manage your battery based on the capacity of that one cell. If you figure out when that cell starts to run away (maybe battery voltage is 13.7V for example) and only charge to there (set in your charge controller(s)). A cell balancer may help. You really need to stop charging before hitting your BMS disconnect (its like a parachute, you don't want to land this way everyday, or ever if possible).
Maybe you can get "enough" capacity from your battery this way. Good luck.
Maybe you can get "enough" capacity from your battery this way. Good luck.
MisterSandals
Participation Medalist
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Increasing voltage loss on higher amps indicates a bad connection. With low (basicly no) current flowing through a resistor (eg a 10 ohm) there barely any voltage drop. BMS is drawing almost no current for voltage measuring..
When pulling a few amps through a resistor voltage drop occrus.
Apart from top balance and proper torquing, did you clean/sand the busbars and terminals?
In doubt of a bad cell? Swap cells, see if the issue moves with it (thus confirming the issue is still with the same cell, even on a different location)
If not, or another cell causes issues -> connection problem.
If you have a FLIR, you can try to draw a high current, bad connections will generate heat and that will be easily spotted with a flir camera.
(But 5A isn't a huge load, I prefer using an inverter or so and draw 50+ A,)
When pulling a few amps through a resistor voltage drop occrus.
Apart from top balance and proper torquing, did you clean/sand the busbars and terminals?
In doubt of a bad cell? Swap cells, see if the issue moves with it (thus confirming the issue is still with the same cell, even on a different location)
If not, or another cell causes issues -> connection problem.
If you have a FLIR, you can try to draw a high current, bad connections will generate heat and that will be easily spotted with a flir camera.
(But 5A isn't a huge load, I prefer using an inverter or so and draw 50+ A,)
Shale MacGregor
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The other issue would be if you charged them without the proper torque
My quick story: Brand new EVE cells and I top balanced them, put them in use and had several runaways. One of them I torqued down more and it fixed the voltage by a lot. Still the issues compounded since my BMS only balances at 50ma, so pain in the ass, I top balanced them again paying special attention to torque. Now back in service after a dozen or so cycles, they are all within .0001-.0004 whenever I check them.
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